There are many well-known varieties of feminine hygiene products configured for the absorption of human body fluids. Some of these absorbent articles, such as sanitary napkins and panty liners, have a pair of wings or flaps that extend laterally from the longitudinal side edges of an absorbent, central portion and are intended to be folded around the crotch area of the wearer's undergarment during use.
In the manufacturing process of these absorbent articles, a continuous web of layered materials typically is driven through a high-speed machine to form several hundred articles per minute. The web may be formed, for example, from a pair of thin, continuous layers (a backsheet and a topsheet) of a polymer film and/or non-woven web that retain a series of individual, pad cores that are spaced evenly apart along the longitudinal axis of the web. The process may include cutting each absorbent article from the continuous web of material, folding the pair of wings around the central portion, applying an adhesive to a release tape, and attaching the release tape to the wings (not necessarily in that order). The wearer removes this release tape to expose the adhesive that has transferred to the backsheet in order to attach the wings to the undergarment.
During the step of folding the pair of wings around the central portion, the article may be conveyed over one or more stationary, contoured rails, which are known in the art as folding plows or folding boards. The folding plows gradually fold each wing 180 degrees from the original plane of the conveyed, web material. Ideally, the wings are consistently folded along fold lines that are parallel to the longitudinal axis of the article so that the free ends of the folded wings come together approximately edge-to-edge. The free ends are aligned adjacent each other and desirably there is no gap or open space between the free ends.
Unfortunately, sometimes during the folding step, one or both of the wings of an article are folded into a skewed configuration, thereby resulting in a gap between the edges of the free ends of the wings. Generally, manufactured articles having this “skew” also may be excessively wrinkled or may have irregular folds. Similarly, one or both wings may fold-over on itself, either inwardly or outwardly. In either the skew or the fold-over situation, it is possible for some of the adhesive on the release tape to transfer to the topsheet that eventually comes into contact with the wearer's body, causing her considerable discomfort.
Accordingly, there is a need for an improved inspection system and process to inspect for wing-folding skew and fold-over of absorbent articles as they are manufactured, whereby any gap or over laid condition can be consistently detected.
Conventional methods for inspecting absorbent articles manufactured from a continuous web and detecting folding process variations in a cost-effective manner have been only partially successful. Many manufacturers use vision systems to produce an image from a composite article undergoing inspection and then analyze the image to detect the position of one or more components within the image. The position of the components are then compared to ideally desired positions to determine whether one or more components are properly positioned. Such an inspection system typically employs conventional video cameras for capturing visual and ultraviolet light that is reflected by and/or transmitted through components of the composite article in order to produce images of the components. After producing an image of the composite article, the image is analyzed to determine whether the components are properly positioned and registered with one another. Other inspection systems employ infrared detectors for producing infrared images of products ongoing formation by sensing infrared radiation emitted by heated components. These images are then compared with reference information to determine, for example, whether the product and components are properly positioned. Such systems are not well suited to inspecting products which have cooled, or which were never heated in the first instance. Still other systems attempt to identify overlapping engagement of panels which are irradiated with radiation. In such systems, an image is produced from radiation received from the irradiated panels. A position of the underlying edge is identified in the image and the underlying edge is compared with preexisting data to determine whether the underlying edge is present and/or properly positioned in the composite article. Such systems are not well suited for determining the presence and/or position of numerous components underlying other components or various components which are somewhat opaque to visible light. Additionally, these systems do not differentiate between gray scales.
Accordingly, there is a need for an improved vision system and method of inspecting and analyzing composite articles during manufacture, especially for identifying gap or skew or fold-over conditions between multiple components in an absorbent article through use of a cascading inspection system.